The present invention relates to a photomultiplier tube unit designed to detect through multiplication weak light radiated onto a faceplate. The present invention also relates to a radiation detector using this type of photomultiplier tube unit.
Conventional photomultiplier tubes are described in Japanese Unexamined Patent Application Publication Nos. HEI-5-290793 and HEI-9-306416. The photomultiplier tubes described therein include a metal side tube having a polygonal cross-section with a flange portion protruding laterally from the bottom of the tube. Similarly, the metal stem plate is provided with a flange portion that protrudes laterally. The flange portions of the side tube and stem plate overlap and are fused through resistance welding to form a hermetically sealed vessel. When using the photomultiplier tube thus constructed in a radiation detector (such as, gamma camera), a plurality of the photomultiplier tubes are arranged in a matrix formation within the detector while confronting the faceplate of each photomultiplier tube with the scintillator.
However, when a plurality of photomultiplier tubes are arranged two-dimensionally in the detector, the flange portions of the photomultiplier tubes interfere with the use of the tube. Arranging a plurality of photomultiplier tubes closely together will form dead spaces in the flange portions. As a result, a gap is formed between adjacent faceplates, causing light detection efficiency to lower.
The present invention has been made to solve the above-described problems, and accordingly it is an object of the present invention to provide a photomultiplier tube unit including a plurality of photomultiplier tubes densely assembled and thereby having an improved light sensing efficiency. Another object of the present invention is to provide a radiation detector with an improved performance.
The photomultiplier tube unit according to the present invention uses a plurality of photomultiplier tubes that are juxtaposed wherein each of the plurality of photomultiplier tube includes a faceplate, a photocathode for emitting electrons in response to light incident on the faceplate, an electron multiplying section, disposed inside an airtight vessel, for multiplying the electrons emitted from the photocathode, and an anode for outputting an output signal based on the electrons multiplied by the electron multiplying section. The airtight vessel includes: a metal stem plate for fixedly supporting the electron multiplying section and the anode with stem pins; a metal side tube with the stem plate fixed on one open end, and enclosing the electron multiplying section and the anode; and a faceplate fixed on the other open end of the metal side tube, wherein a plurality of airtight vessels are juxtaposed and outer surfaces of the plurality of airtight vessels are in facial contact with one another each outer surface being perpendicular in entirety to the corresponding photocathode.
Because the photomultiplier tube is constructed so that the outer surfaces of the metal side tubes are in facial contact with one another, wherein each outer surface is perpendicular in entirety to the corresponding photocathode, a high-density arrangement of the photomultiplier tubes can be achieved. Furthermore, the side tubes of the respective photomultiplier tubes can be electrically connected and the side tubes can be easily made equipotential. As a result, it is unnecessary to electrically connect the stem pin to the side tube of each photomultiplier tube, facilitating the assembly of the photomultiplier tube unit. When a required photomultiplier tube in a device (e.g., a gamma camera) having thus-united multiple photomultiplier tubes is replaced with a new one, the troublesome work of replacing photomultiplier tubes one by one is obviated, simplifying the replacement work.
It is preferable that the plurality of airtight vessels be arranged and fixed on a single substrate. The photomultiplier tubes are arranged on the substrate so that not only is it easy to align the photomultiplier tubes but the alignment accuracy is also improved. Moreover, the management of the number and the arrangement of the photomultiplier tubes in one unit can be performed depending on the shape of the substrate, so the maintenance and the management on a unit basis can be easily done.
It is also preferable that the substrate be formed with a plurality of pin holes for allowing the stem pins to be inserted therein. With the use of such a structure, the photomultiplier tubes can be accurately aligned on the substrate by a simple procedure such that the stem pins of each photomultiplier tube are inserted into the corresponding pin holes.
It is also preferable that the substrate be provided with a plurality of socket pins having an upper portion formed with a concave portion for allowing the stem pin to be inserted therein. With the use of such a structure, the photomultiplier tubes can be accurately aligned on the substrate by a simple procedure such that the stem pins of each photomultiplier tube are inserted into the corresponding concave portions of the socket pins.
It is preferable that the outer surfaces of the side tubes be in facial contact with one another via an electrically conductive adhesive. With the use of such a structure, the side tubes of the photomultiplier tubes can be fixed simply and accurately. Further, the side tubes can be electrically connected with accuracy. As such, the device of an anti-vibration structure can be provided.
According to another aspect of the present invention, there is provided a radiation detector including a scintillator for emitting fluorescent light in response to radiation generated from an object of analysis, a plurality of photomultiplier tubes, each having a faceplate disposed in opposition to the scintillator, for outputting electric charges based on fluorescent light emitted from the scintillator, and a position calculating section for performing calculations on the electric charges output from the plurality of photomultiplier tubes and outputting positioning signals of radiation issued from the object of analysis. Each of the plurality of the photomultiplier tubes includes: a faceplate; a photocathode for emitting electrons in response to light incident on the faceplate; an electron multiplying section, disposed inside an airtight vessel, for multiplying the electrons emitted from the photocathode; and an anode for outputting an output signal based on the electrons multiplied by the electron multiplying section. The airtight vessel includes: a metal stem plate for fixedly supporting the electron multiplying section and the anode with stem pins; a metal side tube with the stem plate fixed on one open end, and enclosing the electron multiplying section and the anode; and a faceplate fixed on the other open end of the metal side tube. The radiation detector includes a photomultiplier tube unit in which a plurality of airtight vessels are juxtaposed, and outer surfaces of the plurality of airtight vessels are in facial contact with one another each outer surface being perpendicular in entirety to the corresponding photocathode.
Because the photomultiplier tube unit for use in the radiation detector is constructed so that the outer surfaces of the metal side tubes are in facial contact with one another, wherein each outer surface is perpendicular in entirety to the corresponding photocathode 3a, a high-density arrangement of the photomultiplier tubes can be achieved. Furthermore, the side tubes of the respective photomultiplier tubes can be electrically connected and the side tubes can be easily made equipotential. As a result, it is unnecessary to electrically connect the stem pin to the side tube of each photomultiplier tube, facilitating the assembly of the photomultiplier tube unit. When a required photomultiplier tube in a device (e.g., a gamma camera) having thus-united multiple photomultiplier tubes is replaced with a new one, the troublesome work of replacing photomultiplier tubes one by one is obviated and the replacement work can be accomplished at a high speed. When the photomultiplier tube is disposed in such a manner that the faceplate is disposed in opposition to the scintillator, a high-density arrangement and easy assembly of the photomultiplier tubes can be achieved, thereby enhancing the property of the radiation detector.
It is preferable that the photomultiplier tube unit be such that a plurality of airtight vessels are arranged and fixed on a single substrate. With the use of such a structure, assembling and replacement of the photomultiplier tubes are performed on a substrate basis, reliability of the entire device is maintained. With the use of the substrate, the alignment accuracy can be improved. Moreover, the management of the number and the arrangement of the photomultiplier tubes in one unit can be performed depending on the shape of the substrate, so the maintenance and the management of the photomultiplier tube in the radiation detector can be easily done.
The photomultiplier tube unit according to the present invention is constructed as described above, an improved light sensing efficiency can be achieved with a high-density arrangement of the photomultiplier tubes. The radiation detector according to the present invention uses the above-described photomultiplier tube unit, so that performance of the radiation detector can be improved.